GameLift Dedicated Server Error and Crash (Failed to find an existing connection with a matching cookie)

Question

I am developing an Unreal Engine multiplayer game (using Unreal Engine 5.0.3), and am hosting the game through a dedicated server (using AWS GameLift). I am using seamless travel with a transition map to travel to the map. However, on certain occasions, I get these warnings (in the server logs):

```
2023.06.21-16.43.37:167][702]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.37:367][708]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.37:605][715]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.37:806][721]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:007][727]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:208][733]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:420][739]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:632][745]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:843][751]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:876][752]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:876][752]LogHandshake: SendConnectChallenge. Timestamp: 175.038124, Cookie: 004170167178014148136175054212228191191000217244032119217029
[2023.06.21-16.43.38:944][754]LogNet: NotifyAcceptingConnection accepted from: 31.10.168.238:10037
[2023.06.21-16.43.38:944][754]LogHandshake: SendChallengeAck. InCookie: 026126161020057175033115175241157071186129109154207249125191
[2023.06.21-16.43.38:944][754]LogNet: Finding connection to update to new address: 31.10.168.238:10037
**[2023.06.21-16.43.38:945][754]LogNet: Failed to find an existing connection with a matching cookie. Restarted Handshake failed.**
```
The server process then crashes, and these messages appear in the server logs:
```
**[2023.06.21-17.27.41:680][526]LogNetPackageMap: Error: GetObjectFromNetGUID: Failed to find outer. FullNetGUIDPath: [7]/Game/_Game/Maps/TransitionLevel.[5]TransitionLevel
[2023.06.21-17.27.41:682][526]LogNetPackageMap: Error: GetObjectFromNetGUID: Failed to find outer. FullNetGUIDPath: [7]/Game/_Game/Maps/TransitionLevel.[5]TransitionLevel.[3]PersistentLevel
[2023.06.21-17.27.41:683][526]LogNetPackageMap: Error: GetObjectFromNetGUID: Failed to find outer. FullNetGUIDPath: [7]/Game/_Game/Maps/TransitionLevel.[5]TransitionLevel.[3]PersistentLevel.[8]PhaseBP_C_2147478607**
[2023.06.21-17.27.41:688][526]LogNet: Warning: UNetConnection::ReceivedPacket - Too many received packets to ack (256) since last sent packet. InSeq: 4978 [UNetConnection] RemoteAddr: 31.10.168.238:10023, Name: IpConnection_2147478641, Driver: GameNetDriver IpNetDriver_2147482464, IsServer: YES, PC: BP_ShooterPlayerController_C_2147478637, Owner: BP_ShooterPlayerController_C_2147478637, UniqueId: EOSCore:17aa7647f4d74a6285324eef980d9520|000232d2374b414cb9ca55a669e72476 NextOutGoingSeq: 11504
[2023.06.21-17.28.44:022][526]LogWindows: Could not start crash report client using ../../../Engine/Binaries/Win64/CrashReportClient-Win64-Debug.exe
[2023.06.21-17.28.44:022][526]LogMemory: Platform Memory Stats for WindowsServer
[2023.06.21-17.28.44:023][526]LogMemory: Process Physical Memory: 2048.76 MB used, 2055.51 MB peak
[2023.06.21-17.28.44:023][526]LogMemory: Process Virtual Memory: 2006.35 MB used, 2007.57 MB peak
[2023.06.21-17.28.44:023][526]LogMemory: Physical Memory: 6746.73 MB used,  932.88 MB free, 7679.61 MB total
[2023.06.21-17.28.44:023][526]LogMemory: Virtual Memory: 6980.73 MB used,  2554.88 MB free, 9535.61 MB total
[2023.06.21-17.28.44:023][526]LogWindows: Error: === Critical error: ===
[2023.06.21-17.28.44:024][526]LogWindows: Error:
[2023.06.21-17.28.44:024][526]LogWindows: Error: Fatal error!
[2023.06.21-17.28.44:024][526]LogWindows: Error:
[2023.06.21-17.28.44:024][526]LogWindows: Error:
[2023.06.21-17.28.44:034][526]LogExit: Executing StaticShutdownAfterError
```

Note that this error doesn’t always occur. On certain occasions, everything works fine and the process doesn’t crash. So this crash happens intermittently.
I can provide the full logs to someone if you provide me with your email.
What is happening here?

Answer

Hi,

```
**[2023.06.21-16.43.38:945][754]LogNet: Failed to find an existing connection with a matching cookie. Restarted Handshake failed.**
```

This seems like a custom log emitted by your Unreal game server. Is there an associated call or failure with GameLift that is leading to this? If so could you share more details regarding that. If this is an Unreal specific issue I'd recommend reaching out on the Unreal Engine forums to see if someone may have insight into this.

Thanks!

GameLift Dedicated Server Error and Crash (Failed to find an existing connection with a matching cookie)

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